, nicknamed Niku (), is a trans-Neptunian object that has an unusual 110 ° tilted solar orbital plane and retrograde orbit around the Sun. While the object has not received a formal name, it received the moniker "Niku" (逆骨), meaning "rebellious" in the

Chinese language Chinese (, especially when referring to written Chinese) is a group of languages spoken natively by the ethnic Han Chinese majority and many minority ethnic groups in Greater China. About 1.3 billion people (or approximately 16% of the wor ...

, by its discoverers.

Details

was discovered by the Mount Lemmon Survey on 31 May 2011. Its rediscovery was announced in August 2016 by a team of astronomers using the Pan-STARRS telescope. It was soon linked with a supposed prograde

centaur A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as being ...

(; inclination = 38° and semi-major axis = 28 AU) that had been lost due to a short

observation arc In observational astronomy, the observation arc (or arc length) of a Solar System body is the time period between its earliest and latest observations, used for tracing the body's path. It is usually given in days or years. The term is mostly use ...

. is in a 7:9

resonance Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...

with Neptune. Currently it is the only object with a nearly polar orbit that is in resonance with a planet. Notably, it is part of a group of objects that orbit the Sun in a highly inclined orbit; the reasons for this unusual orbit are unknown as of August 2016. The orbital characteristics of have been compared to those of (Drac). The orbits of , , , , , , appear to occupy a common plane, with three in prograde and three in retrograde orbits. The probability of this alignment occurring by chance is 0.016%. These orbits should leave a common plane in a few million years because the precession of prograde and retrograde orbits are in opposite directions. Simulations including the hypothetical

Planet Nine Planet Nine is a hypothetical planet in the outer region of the Solar System. Its gravitational effects could explain the peculiar clustering of orbits for a group of extreme trans-Neptunian objects (ETNOs), bodies beyond Neptune that orbit t ...

did not maintain a common orbital plane and the plane does not coincide with the plane of the predicted high-inclination large semi-major axis objects of that model. Other simulations with a few Earth-mass dwarf planet on a high-inclination orbit also failed to reproduce the alignment.

References

External links

* {{DEFAULTSORT:471325 Trans-Neptunian objects Centaurs (small Solar System bodies) Damocloids Discoveries by MLS 20110531 Minor planets with a retrograde orbit